W terminal on Alternator

[WayneS]

Can anyone tell me how many pulses I can expect off the w-terminal for each rev of the alternator.

I am fitting an electronic rev-counter and need to configure it.

Cheers

Wayne

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[Alex_Blackwood]

Frequency - The number of pulses is determined by the speed of the alternator and the number of PAIRS of poles.
The formula is: Frequency = RPM/60 x PAIRS of poles.
Obviously you need to know two things: The RPM of your alternator and the NUMBER of PAIRS of POLES. Example with 2 pairs of poles at 1 RPM = 0.033 hertz.(cycles/second).
at 1500 RPM = 50 Hz.
Sorry without any figures to work on I can't be more help but hope the above gives you some thing to work on.

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[paulrossall]

Another way to solve your problem is to borrow a hand held rev counter which you place against the centre of the flywheel and then you adjust the settings on the rev counter until it reads the correct number of revs. I am told you can hire these instruments from a good hire shop.

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[Alex_Blackwood]

Further to my previous post. You may be able to determine the number of pairs of poles in your alternator by the folowing method. If you connect a multimeter on the resistance (ohms) range across the W terminal and earth you will get a reading.
If you turn the alternator by hand the reading should change as the field magnets line up with the phase windings. If you get four changes of reading in one Rev. then you have a two pole machine. (You will be getting two positve going and two negative going pulses). Your tacho may only read the positive going pulses, I don't know, but suspect that may be case.
Can't guarrantee the above but I would try it. Sorry I can't tell you what readings to expect but what you are interested in is any change in the value.


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